In most all-purpose two-cycle engines used as a power source in small vehicles and working machinery for agriculture and forestry, etc., fuel is supplied by means of a diaphragm type carburetor equipped with a constant-fuel chamber. The constant-fuel chamber is separated from the atmosphere by a diaphragm which adjusts fuel introduced from a fuel pump to a constant pressure, and feeds the fuel into the air intake passage.
In such diaphragm type carburetors, a means (generally a manual starting pump) for feeding out an extra amount of fuel into the air intake passage prior to the starting of the engine or for introducing a prescribed amount of fuel into the constant-fuel chamber, is provided in addition to the ordinary main fuel system and low-speed fuel system. The extra fuel thus provided improves the starting characteristics of the engine at low temperatures.
Carburetors equipped with such starting pumps typically include suction-type carburetors in which the action of the starting pump causes the fuel to flow from the fuel tank, through the fuel pump, into the constant-fuel chamber (or air intake passage), and finally to the starting pump. An example of a suction-type carburator is described in Japanese Patent Application Kokai No. Sho 55-69748), herein incorporated by reference. Push type carburetors operate by pushing the fuel from the fuel tank to the starting pump, into the fuel pump, and then to the constant-fuel chamber (or outside overflow). An example of such a system as seen in Japanese Patent Application Kokai No. Sho 47-38218, is incorporated herein by reference.
When the engine is cranked with starting fuel collected in the air intake passage or constant-fuel chamber as described above, the starting fuel flows toward the engine as a result of the negative pressure of the intake air. However, at low temperatures, the evaporization of the fuel is difficult and this flow becomes liquid flow. The liquid flow is propagated along the walls of the air intake passage or the walls of the intake manifold requiring a large quantity of starting fuel, especially at extremely low temperatures.
One conceivable method of dealing with this problem in a carburetor in which starting fuel is caused to flow out and collect in the air intake passage is to vary the number of times that the starting pump is operated depending on the engine temperature. However, a high degree of precision is required to cause an appropriate amount of starting fuel to flow out and collect in the air intake passage; accordingly, such a method is not generally practical. Also, another problem for systems in which starting fuel is accumulated and held in the constant-fuel chamber is the extremely small diameters of the idle port and main nozzle which cause the fuel to be sucked out into the air intake passage by the negative pressure of the intake air. As a result, the necessary amount of starting fuel cannot be supplied to the engine unless cranking is repeated numerous times.
The present invention solves the abovementioned problems encountered in conventional starting fuel supplying means in which cranking is performed after a starting pump is operated to improve cold starting performance by accumulation starting fuel in the air intake passage or constant-fuel chamber. In particular, the present invention solves the difficulty of maintaining an appropriate amount of starting fuel in the air intake passage, and prevents the need to perform cranking numerous times in order to suck the necessary amount of starting fuel out of the constant-fuel chamber. The present invention provides an easy-to-operate starting fuel supply device which makes it possible to supply the necessary amount of starting fuel held in the constant-fuel chamber to the engine in a short time so that low-temperature starting can be easily and reliably accomplished without the need for any particular skill.